Animal cell cultures may be used as cellular factories for the production of bioproducts. Significant efforts have been dedicated to the development and optimization of animal cell-culture conditions to increase the titer of the final product. In the case of specific antibodies, improving specific antibody productivity in mammalian cell cultures may be achieved with hyperosmotic stress, which can be easily induced by the addition of salts or sugars to a culture medium (Sharfstein 2007). The effect of hyperosmotic stress in increasing specific antibody production has been observed in many hybridoma cell lines and in Chinese hamster ovary (CHO) cells (Ozturk 1991; Oh 1995; Ryu 2000; Kim 2002). The majority of the studies on hyperosmotic stress in mammalian cell cultures observed an approximately two-fold increase in specific antibody productivity; however, the increase in specific productivity was not accompanied by an increase in overall yield because the maximum viable cell density was significantly decreased at higher osmolalities. In a study of the function of glycine betaine as an osmoprotectant, it was demonstrated that glycine betaine can alleviate the growth repression observed in osmotically stressed cultures and can thereby improve antibody production (Øyaas 1994). Several reports concluded that metabolism, cell growth, cell density, product secretion, and specific antibody productivity in mammalian cells are strongly affected by osmotic conditions (Ozturk 1991; Kim 2002).
Viral production in cell systems is the result of two consecutive phases: the growth phase and the virus production phase. Production yield is not only determined by cell physiological state in the virus production phase, but also by the history of the cells as a consequence of cell culture environment during the growth phase. Determination of optimal conditions that maximize viral production yield is not obvious. Thus, in contrast to the effect of hyperosmotic pressure on specific antibody production, specific adenovirus productivity in HEK 293 cells was inhibited when both the cell growth and virus production phases were carried out in hyperosmotic media (Ferreira 2005) or when the cells were grown in isotonic media and the virus was produced in hyperosmotic media (Shen 2010) (note: the osmolality of isotonic media is 290 mOsm; the osmolality of most commercial media is near isotonic). Also, the volumetric productivity of retroviruses was generally lower at elevated osmolality, although the stability of retroviral vectors was enhanced under hyperosmotic conditions (Coroadinha 2006). The effect of osmotic stress on adenovirus production has not been extensively studied, and its utilization to improve viral production yields has not been reported.
There remains a need in the art to develop new methods for producing viral vectors in cells that can result in improved viral production yields.